The present invention relates generally to a tracking and locating radar apparatus and, more particularly, to a radar target location and tracking apparatus utilizing a dual-interleaved pulse train radar waveform.
The state of the art of radar target location and tracking apparatus is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 3,646,588 issued to Van Popta on Feb. 29, 1972;
U.S. Pat. No. 3,935,572 issued to Broniwitz et al on Jan. 27, 1976; and
U.S. Pat. No. 4,746,922 issued to Prenat on May 24, 1988.
The Van Popta patent is directed to a device for making predictions and corrections in azimuth and a given second coordinate (particularly the range) of a target to be tracked from video signals detected by a pulse radar apparatus. In such a device a varying number of bits is written in a buffer register for each detected video signal. The number of storage elements of that register correspond with the number of increments into which the measuring range is divided. These increments are shorter than the pulse duration. The contents of the register are placed in the store of a computer during each transmitter pulse interval. The real target position is obtained by selection of a group of bits from the total of bit positions as written in the store during consecutive transmitter pulse intervals and by logically processing said group of bits.
The Broniwitz et al patent discusses a pulse-doppler radar tracking system which employs four filter channels for tracking range, velocity, azimuth and elevation. Each channel is mechanized in a Kalman filter form by a stored program in a digital computer. The range channel estimates target range rate and acceleration from one of many received signal frequency spectra at multiples of the pulse repetition frequency. Once the error in the range rate estimate is within a velocity corresponding to .lambda.PRF/4, the velocity channel is reinitialized with a correction computed velocity.
The Prenat patent describes a method of and a device for removing range ambiguity in a pulse Doppler radar and to a radar including such a device especially for missile guidance. On tracking operation at a high pulse repetition frequency the method consists in switching the repetition frequency f.sub.R (k) for each time interval .DELTA.t, over a new value f.sub.R (k+1) obtained in a circuit from the measured ambiguous range y(k) and from the ambiguity number (k), as estimated in a circuit from radar information supplied by the radar, in order to remove eclipsing, to maintain the ambiguity number constant and to estimate the range with a growing accuracy in the course of the tracking operation.
A radar system for the detection of moving targets normally employs a waveform designed so target location is available at detection. Data processing is then necessary only to associate target detections from scan to scan, smooth the detection data, and generate velocity information for each target. In short, data processing is necessary only to perform conventional tracking functions.
A radar system normally employs a waveform that consists of a single pulse train or multiple pulse trains used alternatively. The pulse trains are designed so data processing can easily yield range and angle, unambiguously specifying the target's position for each target detection. This information is passed to the data processor, which sorts the detections by target and filters the detections for each target using a standard smoothing scheme (an .alpha.-.beta. or Kalman filter). This smoothing scheme has three purposes:
1. It filters measurement noise so target location can be determined more accurately.
2. It estimates the velocity of each target.
3. It uses the position and velocity estimates to predict future position, facilitating association and sorting of subsequent detections into existing target track files.
In FIG. 1, there is a block diagram of a typical prior art radar tracker apparatus which performs the functions listed above.
Most radar systems do not perform significant Doppler processing. Such processing is typically used for crude discrimination of targets of interest from slow-moving targets (ground traffic, birds) and clutter. It generally is not used for association, sorting, or filtering purposes, especially when simple .alpha.-.beta. filters are used.
While the above-cited references are instructive, there still remains a need to provide a radar target locating and tracking apparatus which utilizes a non-ideal waveform to unambiguously locate targets. The present invention is intended to satisfy that need.